How to remap (mmap) an address allocated with alloc_vm_area ?

Shadew · 02-26-2013, 09:33 AM

Hello,

I'm trying to access to the kernel memory space from a user application. To achieve this, I'm using the customization of the mmap function.

I'm working with Xen and the pages I want to share are from dom0. I first allocated a memory space with alloc_vm_area :

Code:

v_start = alloc_vm_area(PAGE_SIZE*NUM_ALLOC*PAGES_PER_ALLOC,NULL);

if(v_start==0){
    printk(KERN_INFO "Problem allocating page\n");
    return -EFAULT;
}

and then I put pages from dom0 in this space :

Code:

if(HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, ops, NUM_ALLOC*PAGES_PER_ALLOC)){
    printk(KERN_INFO "Hypervisor map grant failed\n");
    free_vm_area(v_start);
    return -EFAULT;
}

Finally, I implement the mmap file operation :

Code:

static int mmap_mmap(struct file * filp, struct vm_area_struct * vma){
        int ret;
        const size_t length = vma->vm_end - vma->vm_start;

        printk(KERN_INFO "Length : %lu, pages : %lu \n", length, length/PAGE_SIZE);

        if(length > NUM_ALLOC * PAGES_PER_ALLOC * PAGE_SIZE){
                printk("Request for a chunk of memory bigger than the available memory\n");
                return -EIO;
        }

        if((ret = remap_vmalloc_range(vma, v_start->addr, 0))<0){
                printk(KERN_INFO "Error in remap_vmalloc_range");
                return ret;
        }

        printk(KERN_INFO "MMaped\n");

        return 0;
}

I used a nod file to link applications with my module. I made a call to mmap in an application :

Code:

vadr = mmap(0, getpagesize(), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);

but the remap_vmalloc_range function failed and it returns the error :
mmap: Invalid argument
Does someone know how to remap such a memory space please ?

Thank you.